There is an urgent need at military-forward operating bases (FOB) for both: (a) disposal of waste; and (b) generation of electricity. Currently, the waste produced from operations, supply depots, commissaries, cafeterias, medical facilities, etc is being simply burned in open pits. This practice exposes the troops and military support personnel to toxics, pathogens, etc., provides a very clear infra-red signature, and leaves environmental problem trails. Hauling the waste out from the FOBs with long truck convoys exposes troops and truck operators to being attacked. The record here is horrible with more personnel being lost in the waste hauling operations than at the front lines. Also hauling in fuel to run generators to recharge the myriad of batteries used for the advanced instrumentation and communications assets has a similar convoy death record.
Domestically, there are problems from waste disposal as well in underdeveloped regions, stressed urban areas, and very remote areas of oil and gas exploration and production operations, medical facilities, emergency cleanup, etc. as well.
What is needed is a small portable module that can be air dropped or trucked in that will use these waste streams to produce electric power. Various embodiments of the present invention address these needs.
The synthetic production of hydrocarbons by the catalytic reaction of carbon monoxide and hydrogen is well known and generally referred to as the Fischer-Tropsch (FT) reaction. The FT process was developed in the early 1920's in Germany. It has been commercial since World War II, particularly in South Africa. The FT reaction benefits from a catalyst to convert the carbon monoxide (CO) and hydrogen (H2) to a range of paraffinic hydrocarbons from 1 to 100 carbons.
Numerous types of reactor systems have been used for carrying out FT synthesis ranging from fixed bed three phase bubble column designs, fluidized bed, ebullating beds, and fixed plate heat exchangers. These various designs may encounter high expense due to large amounts of catalyst used from inefficient contact with the catalyst surface, and ineffective cooling.
Fixed bed reactors of individual catalyst particles ae packed into tubes arranged in a cylindrical vessel. The individual particles can involve various shapes of spheres, cylinders, saddles, and rings with void volume fractions from 0.3 the 0.5. Although these packed bed reactors are simple and can be scaled up, they encounter high heat release requirements with the tube size being small with high pressure drop. Also, these narrow tubes are difficult to clean and maintain.
The manufacture of finned tubes for heat exchangers is used in some designs. Modern extrusion technology can produce tubes with a wide variety of cross-sections and alloys.
Some FT reactors include a tube packed with extended surface materials (I.e. Beryl saddles, etc.) which are coated with the catalyst. The syngas flows inside the tube while the coolant flows on the outside of the tube. The tube internal diameter should be more than 3 inches to radially extract the heat, and the packing should be small size to avoid a wall affect, but a small packing size can produce pressure drops. So the reactor may not efficient from the ratio of surface area to volume standpoint. There is also the challenge that at the contact points the FT liquids can gather and form hard paraffin wax resin blockages which can require the bed to being cleaned or replaced often. Another approach is to use a larger tube and irrigate the column of pack catalyst pellets with the FT liquid or a solvent to carry the heat away from the catalyst packing—such a reactor is termed “trickle phase”. This benefits from a uniform distribution of liquid to avoid hotspots and running the risk of forming resin blockages which create further hotspots and sometimes cause reactor run away.
Plate heat exchangers had been used with narrow spacing between the plates, in which the plates are coated with a catalyst. This concept achieves a large amount of catalyst surface area in a large reactor that is heat exchanged with the cooling liquid on the other side of the plates; thus, it is not volume efficient and thus expensive to fabricate. There are many variations of the concept of closely spaced plates that are catalyst coated to develop a plate array or matrix heat exchanger, but they can encounter narrow spacing, high pressure drop, flow obstruction and high cost of manufacture.
A more recent design uses commercial air conditioner cores to help cut the cost of manufacture, avoid narrow spacing, and provide a large amount of surface area, but these cores have to be stacked and placed inside of a large reactor vessel and then individually plumbed to the outside. This makes it a complex reactor assembly, a challenge to scale, difficult to maintain, and difficult to clean. And stacked cores have a complex FT liquid downflow around the heat exchange tubing passing through the fins that risks the formation of resin blockages at junction points. Unless the cores are custom manufactured to be large, the reactor does not easily scale up from a small pilot scale to a large commercial scale. This added stacked core complexity makes the maintenance even more challenging.
What is needed are new designs of FT reactors that overcome some of the past problems, and which present novel and non-obvious improvements to the FT process.